In legal terms, “c/o” means “care of” and identifies someone who will receive mail or legal documents on behalf of the actual addressee. You see it on lawsuits, contract notice clauses, tax forms, and any correspondence where the intended recipient doesn’t get mail at the delivery address directly. The person listed after “c/o” is an intermediary, nothing more: they accept delivery and pass the documents along, but they don’t gain any legal authority over the contents just by being named.
What the C/O Intermediary Can and Cannot Do
Naming someone as your c/o contact gives them one job: receiving your mail. It doesn’t make them your lawyer, your agent, or your representative for any other purpose. An attorney listed as c/o on a court filing can accept the envelope, but that alone doesn’t authorize them to act on the case. A registered agent listed as c/o for a corporation can receive service of process because state law separately gives them that authority, not because of the c/o line itself.
People use c/o when the intended recipient doesn’t have a stable mailing address, is trying to keep a home address private, or routes legal mail through a professional. Someone between apartments, a business owner whose mail goes through a registered agent, a domestic violence survivor using a substitute address, a taxpayer whose correspondence flows through an accountant: each situation calls for the same convention.
How to Format a C/O Address
USPS addressing standards put the intended recipient’s name on the top line, “C/O” and the intermediary’s name on the second line, then the street address, then the city, state, and ZIP code. A correctly formatted envelope looks like this:
JANE DOE
C/O ROBERT SMITH
123 APPLE WAY
ANYTOWN, ST 12345
The USPS Domestic Mail Manual confirms this layout in its guidance on shared receptacles and care-of addressing.1USPS. Domestic Mail Manual 508 – Recipient Services The c/o line belongs between the recipient’s name and the street address. Never place it below the street, and never combine it with the city-state-ZIP line. Capitalize “C/O” and put a space before the intermediary’s name. Writing out “In Care Of” carries no different legal meaning than the abbreviation.
On restricted delivery items such as certified mail, registered mail, and similar accountable services, USPS rules permit either the named recipient or the c/o intermediary to sign for delivery.1USPS. Domestic Mail Manual 508 – Recipient Services Private couriers like FedEx and UPS follow their own signature policies, and courts handling service of process apply separate rules about who counts as an authorized recipient.
C/O in Service of Process
Service of process is where the c/o designation carries its heaviest legal consequences. Federal Rule of Civil Procedure 4(e) allows an individual to be served by delivering the summons and complaint to “an agent authorized by appointment or by law to receive service of process.” Rule 4(h) applies a similar standard to corporations, permitting service on “an officer, a managing or general agent, or any other agent authorized by appointment or by law to receive service of process.”2Cornell Law School. Federal Rules of Civil Procedure Rule 4 – Summons When a plaintiff addresses a summons to a defendant “c/o” a registered agent or authorized representative, the c/o line identifies that authorized intermediary.
The Supreme Court held in Mullane v. Central Hanover Bank that due process requires notice “reasonably calculated, under all the circumstances, to apprise interested parties of the pendency of the action and afford them an opportunity to present their objections.”3Justia US Supreme Court. Mullane v. Central Hanover Bank and Trust Co., 339 U.S. 306 (1950) Sending a summons to a c/o address that doesn’t correspond to someone actually authorized to accept service can lead a court to find service defective. Defective service opens the door to a motion to quash, and a default judgment obtained on bad service is vulnerable to being set aside later.
C/O in Contract Notice Clauses
Most commercial contracts include a notice clause that tells each party where formal communications must be sent. These provisions often use “in care of” to route notices through a designated person, such as a general counsel or corporate secretary. A typical clause reads: “Any notice to the Company shall be addressed in care of its Secretary at [address], or at such other address as the Company may designate in writing.”
The c/o designation does two things in a notice clause. It names the person responsible for handling formal communications, and it fixes the address where notice is deemed delivered. If the contract directs notices “c/o the Company Secretary at 100 Main Street” and you send yours to the CEO at a different office, the other side can argue you failed to give proper notice under the agreement, even if the CEO eventually saw the letter. This matters most in cure and termination provisions, where the recipient gets a defined number of days to fix a breach and the clock runs from proper delivery.
When you sign a contract, read the notice clause carefully. If you want communications routed through your attorney, make sure the clause names them with a c/o designation and lists their current address, and update the information promptly when it changes.
C/O on IRS and Government Forms
The IRS uses the c/o format for taxpayers who receive mail through a third party. Form 8822 (Change of Address) instructs: “If you receive your mail in care of a third party (such as an accountant or attorney), enter ‘C/O’ followed by the third party’s name and street address or P.O. box.”4IRS. Form 8822 – Change of Address The same instruction appears on Form 8822-B, which businesses use to update their address or responsible party.5IRS. Form 8822-B – Change of Address or Responsible Party
Keeping this information current matters because IRS deadlines run from the mailing date to the address on file, not from the day you actually see the letter. A notice of deficiency gives you 90 days to petition Tax Court, and that period runs whether or not your former accountant still forwards your mail. Form 8822 is one page and carries no fee.
C/O and Address Confidentiality
The c/o concept underpins address confidentiality programs available in all 50 states. These government-run programs provide victims of domestic violence, stalking, sexual assault, and similar crimes with a substitute mailing address that they use on public records, court filings, and correspondence. The program’s office forwards mail to the participant’s actual location, functioning as a permanent government-backed c/o arrangement.
Outside formal programs, lawyers routinely use c/o to shield clients’ home addresses. In family law cases, an attorney often lists their own office as the c/o address for all court filings so the client’s residence stays out of the public record. Companies do the same by routing legal notices through in-house or outside counsel.
C/O vs. Attn vs. FBO
Three abbreviations get mixed up on legal documents, and they do different things.
- C/O (Care Of) routes mail through an intermediary who forwards it to the intended recipient. The recipient’s name comes first, then “c/o” and the intermediary’s name. Used when the recipient doesn’t receive mail at the delivery address.
- Attn (Attention) directs mail to a specific person inside an organization that already receives mail at that address. USPS Publication 28 places the Attention line above the recipient line — the name of the firm. Used when the organization is the primary addressee but a particular employee should handle the mail.6USPS Postal Explorer. Publication 28 – Postal Addressing Standards
- FBO (For the Benefit Of) appears on financial accounts and instruments to show that assets are held or managed for a specific person’s benefit. A retirement account labeled “ABC Trust Co. FBO Jane Doe” means the trust company manages the account and Jane is the beneficiary. The FBO party typically cannot endorse checks or access funds directly; the custodian handles transactions.
C/o is about mail delivery, attn is about internal routing within an organization, and fbo is about beneficial ownership of assets. Using c/o where attn belongs rarely causes a delivery failure, but using c/o instead of fbo on a financial document misidentifies the legal relationship between the parties.
What Goes Wrong When C/O Is Used Incorrectly
The consequences depend on the setting. In litigation, sending service of process to a c/o intermediary who isn’t authorized to accept it can produce defective service, which delays the case and puts any default judgment at risk of being set aside. In contracts, notice sent to the wrong c/o address may not satisfy the agreement’s notice requirement, which can invalidate a termination or leave a cure period that never started running. On tax filings, an outdated c/o address means statutory notices go to a former intermediary while the response deadline continues to run against you. And in matters involving sealed filings, trade secrets, or protected personal information, misdirected legal mail can expose confidential material to people who were never supposed to see it.